KUOPIO, FINLAND — Although past research has shown a link between sauna use and fewer cardiovascular events, a large prospective study from Finland suggests its use could also help decrease all-cause mortality—and that the associations may be "dose-dependent". The welcome take-home message: the more an individual relaxes in the warmth, the better.
A study including more than 2000 men in Finland, where sauna is more a way of life than in many countries, showed that the rate of sudden cardiac death (SCD) and fatal CHD, fatal CVD, and all-cause mortality 18 years later were all significantly lower for those who used saunas two to three times per week at baseline vs those who only used them once a week. The numbers were even lower for those who participated four to seven times per week.
In addition, the less frequent sauna users had significantly greater risk for all of these events compared with the most frequent users, report Dr Jari Laukkanen (University of Eastern Finland, Kuopio) and associates in a report published online February 23, 2015 in JAMA Internal Medicine.
"We already have many kinds of preventive measures for these occurrences, like physical activity, but it appears that sauna could also be included in this group—especially because it is so enjoyable," Laukkanen said to heartwire .
Dr Rita F Redberg (University of California, San Francisco) writes in an accompanying editor's note that the study did not examine the mechanism for the associations but speculates that it could involve the act of relaxing itself or even just the "camaraderie" of the activity. Whatever the mechanistic action, "clearly time spent in the sauna is time well spent."
A Rare Large Study of Sauna and CV Health
Although researchers from Japan have previously examined associations between sauna use and heart health in several small studies, the current investigators sought to assess more variables in a wider population. "We wanted to conduct a large, long-term study to look at specific risk factors," said Laukkanen.
His team examined data on 2315 male participants from the Finnish Kuopio Ischemic Heart Disease Study who were between the ages of 42 and 60 years (mean age 53.1 years) and were all users of traditional Finnish dry saunas, which usually feature low humidity and high temperatures.
Baseline assessments, conducted from March 1984 through December 1989, checked risk factors such as smoking use, body-mass index, blood pressure, cholesterol, medication use, and physical-activity levels. Self-reported questionnaires also asked about weekly sauna use.
Based on the answers, the investigators created three subgroups: those who reported using the saunas once a week (601), those reporting two to three times per week (1513), and those reporting four to seven times per week (201). Follow-up for the participants ranged from 18.1 to 22.6 years (mean 18.8 years).
Over the long term, the overall group had 190 SCDs, 407 fatal CVDs, 281 fatal CHDs, and 929 deaths from any cause. The group who used saunas most frequently had fewer SCDs vs medium users and less frequent users (5% vs 7.8% and 10.1%, respectively). They also had fewer fatal CHDs (8.5% vs 11.5% and 14.9%), fatal CVDs (12% vs 16.4% and 22.3%), and all-cause deaths (30.8% vs 37.8% and 49.1%).
The adjusted hazard ratio (HR) for SCD for the most frequent and medium users vs the infrequent users was 0.37 (95% CI, 0.18–0.75) and 0.78 (95% CI 0.57–1.07), respectively.
The adjusted HRs for fatal CHD for the groups were 0.52 and 0.77, respectively; for fatal CVD they were 0.5 and 0.73, respectively; and for all-cause mortality they were 0.60 and 0.76 (P for trend for all <0.005).
Length of sauna session also influenced the findings—with sessions lasting longer than 19 minutes associated with a 52% lower risk of SCD vs spending less than 11 minutes in the rooms. Longer time in the activity was also associated with a reduced HR for fatal CHDs and fatal CVDs. In fact, all-cause mortality was the only event not significantly associated with time spent per session.
Overall, the study shows that sauna use is protective against serious cardiovascular events—at least in middle-aged males, write the investigators. "Our results suggest that sauna bathing is a recommendable health habit, although further studies are needed to confirm our results in different population settings," they add.
"I hope this will result in other researchers in other countries studying how heat or this type of exposure may affect the cardiovascular system. We're especially interested in looking into the possible mechanisms behind the associations we found in our study," said Laukkanen.
He noted that it is important for all individuals to incorporate several kinds of lifestyle habits, including healthy diets, not smoking, and exercising regularly. "And sauna is one additional part of a healthy lifestyle."
Enjoyment Instead of "Unnecessary Tests"
Redberg notes that she has often advised patients to spend their money on something they would enjoy instead of on unnecessary tests. "Laukkanen et al present data indicating that my advice would not only help my patients feel good but would also, if they chose to regularly use a sauna bath, help them live longer."
Dr Sumeet S Chugh (Cedars-Sinai Heart Institute. Los Angeles, CA), who was not involved with this research, told heartwire that the study findings "add to a lot of information already out there that suggests lifestyle changes are equally if not more important than any other kinds of medical therapy that we could provide to our patients."
Chugh noted that the study authors were careful to point out limitations, especially that cause and effect were not established. "With those caveats, this is all very interesting," said Chugh. "There is an ocean of information out there that points to physical activity being really closely linked to decreasing disease and death, no matter what the cause is. On the other hand, if I suffer an injury tomorrow and couldn't exercise, then maybe the sauna could be a good option for me."
Chugh pointed out that the "dose-dependent phenomenon" of frequency of use affecting the findings was interesting but also brought up more questions. "Did the people who used the sauna more also do more physical activities? Or were their dietary habits better? Or did they drink less alcohol? That could have skewed the findings as well," he said.
"Also, saunas mimic exercise because the heart rate goes up. But you're not really moving your limbs or doing the things that bring about the benefits of exercise. So for now, we can't really speculate as to why there would be a dose effect," said Chugh. But, "from a practical standpoint, if there are people who cannot exercise for any reason, then this really might be helpful."
The authors have reported no relevant financial relationships.
Heartwire from Medscape © 2015 Medscape, LLC
Cite this: The Joy of Dry Warmth: Saunas May Help Cut CVD Risk - Medscape - Feb 25, 2015.